What is at risk if London floods?

1.5 million people live in the floodplain of the River Thames and its tributaries. Many more people work, visit or travel through these potentially vulnerable areas.

Such a large urban area means there is a rapid response to rainfall within drainage systems. Lots of impermeable surface cover in London, such as concrete on pavements and buildings, means there is a lot of rainfall runoff from the land into drainage systems and London’s rivers. This creates a build up of water and increase the likelihood of fluvial and surface water flooding.

Flooding is one of the greatest risks to London in the 21st century. Climate change alongside urban growth in the capital will increase the risk of flooding in the future. Therefore flood defences need to be improved and management strategies put in place to prevent the city from becoming immersed in flood water in years to come.

As london is a leading global city with strengths in the arts, entertainment, fashion, finance, healthcare, media, research and transport, the effects of flooding would have a national and international impact.

Central and Local Government

London is the seat of government and parliamentary activity for the UK, and the Central Government district of Whitehall is entirely within the Thames floodplain, along with the Houses of Parliament and City Hall, the Greater London Authority’s HQ.

Large areas of Pimlico and Victoria are the site of important government offices. Local authority offices located in areas such as Hammersmith, Tower Hamlets and Newham town halls are also based within the floodplain.

It is hard to place a value on the loss or disruption flooding in these areas would cause but a report by the Environment Agency (2007) suggested the loss of staff time alone in the civil service would cost £10m per day. In spite of continuity arrangements for major crises, such an event could be profound.

Business

London is the UK’s largest centre of economic activity and is often referred to as a leading global financial centre alongside New York and Frankfurt. London is estimated to contribute £250 billion to the UK economy each year.

Although the traditional centre of the ‘square mile’ of the City of London is outside the floodplain of the Thames, rapid development in the Docklands area is entirely within it. The Docklands is well protected against flooding, however the Environment Agency accept that climate change will make existing defended areas more vulnerable over the this century.

The material damage to the skyscrapers located in the area may be relatively small, however the expense of relocation of business and the damage to transport could be significant.

Disruption caused from a serious flood could result in losses for the UK as a whole, notably the tourism industry, as London is not only a popular destination but a stopover for people traveling the country.

New development

The Thames Gateway; Europe’s largest regeneration project and the site for an estimated 200,000 new homes by 2020, is attracting investment in the housing and commercial sectors. As this area is located largely in the floodplain, flood risk is already a concern for developers who aim to ensure new development manages and limit flood risk. Flooding risk to the Thames Gateway has been raised in numerous debates at the House of Commons and continues to be a source of debate.

The London Underground

The Underground is a vital part of London’s infrastructure, with over 1 billion journeys made each year. Much of the central area of the Tube network is based within the floodplain and 38 underground and Docklands Light Railway stations could be at risk.

Short periods of heavy rain, as witnessed on August 2002 in London, can result in surface water flooding, often described as flash flooding, which can disable Tube lines for extended periods. Estimates put the loss of one day’s disruption on the underground at £0.75m.

The London Underground (LU) Environment Report (2006) noted that studies have shown that sections of the underground network are vulnerable to flooding from the River Thames. Incident data from the report shows flooding and adverse weather conditions accounted for 32% of environmental incidents in 2005/6.

Following the London Climate Change Partnership’s study of the effects of climate change on London’s transport system LU undertook an upgrade of the drainage systems on the Jubilee, Northern and Piccadilly lines to help mitigate the risk of flooding at key stations.

The LU Environmental Report (2008) stated that in 2009-2010 LU and the London Climate Change Partnership Transport Working Group will be working on prioritising vulnerable underground stations to ensure that the transport system in London is prepared for the effects of climate change.

Thames Estuary

Thames Estuary 2100 is a flood management plan for London and the Thames Estuary, lead by the Environment Agency. The plan takes into account the impact of climate change, rising sea levels and the natural ageing of flood defence infrastructure to plan and manage flood risk in the region up until 2100.

The usual response to this risk has been to construct fixed, raised defences in the form of walls or embankments, these however do not eliminate the risk of flooding and can often provide a false sense of security or complacency among those living or working in defended areas.

Due to climate change both the chance and consequence of flooding are increasing. Sea level rise, more frequent and higher storm surges and increased winter rainfall and more intense summer rainfall will add to existing risk. The London Flood Response Strategic Plan notes that it may not prove possible to improve fixed defences sufficiently to maintain or raise protection standards.

Floods are natural events that result from either excessive rainfall that leads to rivers overflowing their banks, or from tidal storm surges on the coast or in estuaries such as the Thames Estuary.

The damage and death that can potentially be caused only occur due to the human activity that takes place in river valleys or estuaries where flood water spreads. In urban areas such as London, man-made drainage systems may have inadequate capacity or become blocked leading to further flooding.

Planning Policy Statement 25 – Development and flood risk (PPS25) (LINK TO PPS25 PDF) advises avoiding building on development in flood risk areas, a common concern regarding the ongoing development of the Thames Gateway region.